1. Scope of the Invention
This application relates to novel arachidonic acid derivatives which contain an allene group. More specifically it relates to leukotriene mediating compounds which are allene containing derivatives of arachidonic acid which may also contain chain substituted sulfur or oxygen.
2. Related Art
Australian researchers Kellaway and Trethewie in 1940 described a myotropic substance which was released from the lung during anaphylaxis and could possibly account for some of the anaphylactic symptoms. Studies of purified but unidentified material on guinea pig jejunum demonstrated that the material had a slow contracting effect on smooth muscle. Because of this, the unidentified material was called slow reacting smooth-muscle-stimulating substance (SRS).
The substance resisted identification for many years and it was not until the development of liquid chromatographic separation techniques that it became possible to determine the structure of SRS. In the intervening years between the discovery of SRS and its identification, a goodly number of pharmacological studies were carried out which indicated or suggested that SRS was released during allergic reactions and produces many of the effects experienced by afflicted individuals. Initially the myotropic material released by the lung during anaphalaxis was designated SRS-A to differentiate substance produced by the lungs upon immunological challenge by specific antigens from those generated upon non-immunological stimulation. However, subsequent studies have shown SRS-A and SRS to be one and the same material.
Beginning in the late 60's and continuing into the early 70's much new information was developed on the biochemistry of arachadonic acid, particularly with the successive findings of prostaglandin endoperoxides, thromboxanes and prostacyclin. A recent additive to this list of oxygenated arachadonic acid metalolites are the leukotrienes first described by Borgeat and Samuelsson. These metabolites were named leukotrienes because of their origin from leukocytes and the presence of a conjugated triene. The interest in leukotrienes gained momentum when it was discovered that an SRS substance was a leukotriene.
Early studies into the biosynthesis of arachadonic acid into leukotrienes was carried out by Borgeat, Samuelsson and colleagues, first reported in 1979. These researchers determined that arachadonic acid is converted to a five perhydroxy acid by means of a novel lipoxygenase-type reaction which is seen only in the leukocyte. The disposition of this 5-hydroperoxy acid was determined to be a reduction to the 5-hydroxy acid by a reductase. The second and most important step is that wherein the 5-hydroperoxy acid undergoes loss of water to give a compound known as leukotriene A.sub.4 determined by E. J. Corey to be (.+-.)-5,6-oxido-7,9-trans-11,14-cis-eicosatetraenoic acid. Prior to the discovery of this unstable epoxide matabolite, Borgeat and colleagues reported the biosynthesis of a 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid and 8(S)-hydroxy-9,11,14-eicosatrienoic acid in rabbit peritoneal polymorphonuclear leukocytes (PMNL). An 8,11,14-eicosatrienoic acid also derived from arachadonic acid was reported in this study. Subsequent to this work Borgeat, et al reported the discovery of an arachadonic acid metabolite, the 5-(S),12(R)-dihydroxy-6,8,10,14-eicosatetraenoic acid, subsequently named leukotriene B.sub.4. Still further research by Borgeat and Samuelsson determined the structures of minor metabolites of arachadonic acid in PMNL which were 5,6-dihydroxy-7,9,11,14-eicosatetranoic acids (epimers at C-6) and at 2 geometric isomers of leukotriene B.sub.4 (epimers at C-12).
The broader significance of this newly discovered arachadonic acid biosynthetic pathway was brought to light when B. Samuelsson and R. C. Murphy separately reported that SRS was a leukotriene. With the advent of high pressure liquid chromatography it became possible to purify samples of SRS-A sufficiently so that they could be spectrally characterized. Morris et al, reported that the ultraviolet spectrum of a highly purified SRS-A sample showed the characteristic absorption bands of leukotrienes. At about the same time studies by B. A. Jakschik, et al and P. Sirois, et al suggested a precursor of arachadonic acid in the synthesis of SRS-A. Previous studies had already shown that the ionophore A23187 stimulated the release of SRS from leukocytes and of SRS-A from perfused lungs. It was also known that, under certain conditions, the cyclooxygenase inhibitors indomethacin and aspirin could stimulate the release of SRS-A. Such data reasonably indicated a relationship between SRS-A and leukotrienes because leukotrienes are metabolites of arachadonic acid in leukocytes, the synthesis of the 5-hydroxy acid is not inhibited by indomethacin, the ionophore A23187 is known to be a powerful stimulator for the transformation of arachadonic acid into leukotriene B.sub.4 in human PMNL, and the conjugated triene is a structural characteristic of leukotrienes.
There was also evidence that SRS and SRS-A were sulfur containing compounds. This supposition rested in the observation that many thiols and particularly cysteine stimulated the formation of SRS and SRS-A. Leukotriene A.sub.4, the epoxide was expected to react easily with nucleophiles such as thiols and alcohols. Sulfur labeling experiments where SRS was produced from mastocytoma cells incubated with arachadonic acid, L-cysteine, and ionophore A23187 determine that SRS incorporated cysteine and arachadonic acid. Chemical analysis of this SRS material revealed that the compound was a 5-hydroxy-7,9,11,14-eicosatetraenoic acid carrying a thioether linked substituent at C-6.
Hammarstrom, et al subsequently identified the C-6 substituent in mouse mastocytoma cells SRS as glutathione. This SRS material was determined to be 5(S)-hydroxy-6(R)-S-glutathionyl-7,9-trans,11,14-cis-eicosatetraenoic acid, now recognized to be leukotriene C.sub.4. Glutathione is a tripeptide comprising cysteine, glycine and glutamic acid.
SRS is also known to contain a large amount of another muscle contractant which is even more active than leukotriene C.sub.4. Research into this area by Morris, et al using an SRS material obtained from rat basophil leukemia cells determined the presence of a cysteinylglycinyl conjugate of leukotriene A.sub.4, a 5-hydroxy-6-S-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid. This compound was given the name leukotriene D.sub.4. These same investigators demonstrated that leukotriene D.sub.4 could be prepared by the action. Of gamma-glutamyl transpeptidase on leukotriene C.sub.4. Additional work by Bach, et al, and Morris, et al confirmed that the SRS-A released upon immunological challenge of sensitized guinea pig lungs was identical with the SRS released by the rat basophil leukemia cells.
The distribution of leukotrienes and the biological significance of these compounds has not been fully elucidated to date. Such compounds have been identified in various leucocytes, mast cells, tumors, and lungs but the question still is unanswered as to whether or not these compounds are generally distributed throughout cells like prostaglandins or are limited to cells and tissues more directly involved with allergic reactions. There is tentative speculation that leukotrienes have a broad distribution based on the fact known leukotrienes are found in four different sources and that SRS substances chemically and biologically similar to leukotrienes have been located in many other tissues such as human skin, human nasal polyps, blood vessels, heart, and cat paw, and in a number of other species. However, to date the data from studies in this area do not establish which cell type is tied in with a source of leukotrienes. Immunological challenge does release these substances, therefore suggesting that cells carrying receptors for immunoglobulins E (or G for the guinnea pigs) are likely involved.
Understanding of the biological activity of these materials at this time is based primarily on knowledge generated from studies on SRS and SRS-A. These studies clearly point out the importance of SRS-A in immediate hypersensitivity reactions. Because of the importance of immediate hypersensitivity reactions in medicine, these compounds probably will have biological importance in determining the role of and in treating allergy, anaphylaxis, asthma and other conditions of a similar physiological bases.
The elucidation of the metabolic transformation of arachidonic acid into leukotrienes and their involvement in immediate hypersensitivity reactions provides the jumping off point for a better understanding of the mechanism behind the onset of such diseases as asthma and other diseases attributed or attributable to SRS-A material. With this information, a scientific approach to the treatment of asthma and SRS related problems can be substituted for the imperical approach which has in the past primarily characterized the development of drugs and treatment of such reactions.
With this understanding of the biosynthesis of leukotrienes it is now possible to design treatment regimes to treat immediate hypersensitivity reactions by effecting the synthetic pathway for peptide substituted leukotrienes. Because the biosynthetic pathway comprises a series of enzymatic reactions, it may be possible that drugs can be used to block or influence one or more of these enzymatic reactions. For example, it is known that clinical steroids block the release of arachidonic acid from phospholipids by blocking phospholipase activity. Nonsteroid anti-inflammatory drugs such as aspirin and indomethacin block the cyclooxygenase pathway leading to prostaglandins, thromboxanes and prostacyclin. Another possible approach to the control of leukotriene biosynthesis could be the use of "false-substrates" which would enter the lypoxygenase pathway and be transformed by the enzyme, but could not lead to the formation of active leukotrienes. This latter area is the focus of this invention. Allene containing arachidonic acid derivatives have been developed which can act as false substrates effecting the formation of 5-hydroperoxy acid and thereby mediating an immediate hypersensitivity reaction caused by leukotrienes. In addition the subject compounds may be used to treat inflammatory disease by virtue of their ability to regulate formation of 5-H PETE, the biosynthetic precursor of leukotriene B.sub.4 which as a chemotactic and chemokinetic agent, effects release of lysomal enzymes and increases cyclic nucleotide levels, all key features of cellular inflammation.